Method of drying substrates and use thereof

ABSTRACT

A method is provided for washing, drying, applying a curable coating, and effecting the cure of such coating on a variety of substrates, such as metal, for example steel, plastic and wood. A particularly effective drying procedure based on the generation of a dehumidified and filtered air stream directed substantially parallel to the wet substrate allows for a significant decrease in drying time while maintaining coating effectiveness.

This application is a continuation-in-part of U.S. application Ser. No. 08/783,070, filed Jan. 15, 1997, U.S. Pat. No. 5,718,061 which is a continuation of U.S. application Ser. No. 08/625,068 filed Mar. 29, 1996; U.S. Pat. No. 5,709,038 which is a continuation-in-part of U.S. application Ser. No. 08/423,683 filed Apr. 18, 1995, now U.S. Pat. No. 5,554,416; which is a continuation of U.S. Ser. No. 08/126,547 filed Sep. 24, 1993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of drying substrate, for example metal, such as steel, or plastic and wood, and the subsequent treatment of such dried substrate by various coating techniques. More particularly, an air filtration and drying system is used in the drying stage, comprising a booth in combination with means capable of generating an air stream which is sufficient to expeditiously reduce the moisture level on the substrate surface positioned in the booth. The resulting dried substrate has been found to have improved coating characteristics.

2. Description of Related Art

An air atomizing spray gun is typically utilized to rapidly apply paints, industrial coatings and other finishing products to a wide variety of industrial, commercial and consumer goods. Unfortunately, a profusion of transient, airborne particles and associated fumes, generally designated as overspray, are produced during the application process. To reduce the potentially serious health risks associated with the inhalation and bodily contact of the overspray, spray booths and other collection systems have been designed in accordance with a plethora of strict regulations. These regulations are set forth by the Occupational Safety and Health Administration (OSHA), the Environmental Protection Agency (EPA), the National Fire Protection Association (NFPA) and myriad other governmental regulatory agencies, to collect and effectively treat the discharged air and direct it away from the operators of the spray equipment and other adjacent ancillary personnel. Heretofore, high volume blowers have typically been utilized to draw uncontaminated, ambient air through the coating area, where the air mixes with the overspray, and to duct the air, now contaminated with coating particles and noxious gases, into a treatment area prior to discharge.

A dry filtration system, utilizing arrestor pads, has commonly been employed to remove overspray from the contaminated air stream. As the contaminated air stream passes through an arrestor pad, the larger coating particles impact against the surface of the pad and adhere thereto. As known in the art, the surfaces of the arrestor pad may be covered with an adhesive to facilitate the capture of the coating particles, thereby increasing the capture efficiency of the pad. The proper performance of arrestor pads in removing particles from a contaminated airstream is heavily dependent on frequent operator inspection and regularly performed maintenance. If the required inspections and maintenance are not performed according to specifications, arrestor pad blow by and an unintentional discharge of contaminants to the surrounding environment may occur.

A water-based overspray collection system, commonly designated as a water downfall system, utilizes a cascading curtain of water to remove overspray particles from a collection wall. The contaminated water is temporarily stored in a sump or collection tank and is subsequently pumped through a filter to remove any particles suspended therein. The filtered water may be reused in the water downfall system or may be discharged to a water treatment system or the environment. Prior to any discharge, the water must normally must go through an expensive and time consuming neutralization process, wherein any remaining particles in the water are allowed to sink to the bottom of the collection tank, thereby forming a concentrated sludge or cake that must be removed and disposed of on a regular basis.

The above-described overspray collection systems are moderately effective in the removal of larger overspray particles from the spray booth collection area. Unfortunately, they are not effective in the collection of submicron size particles and gases which are eventually discharged to the outside air, potentially creating an environmental hazard.

Solvent based coatings have commonly been utilized in finishing processes due to the fast drying characteristics of the solvents. As the solvents evaporate, the coating solids suspended therein flow together and form a continuous layer of dry solids. A major disadvantage of solvent based coatings is the explosion hazard created by the inherent flammability of the solvent and the associated solvent fumes which are released during the evaporation process. Additionally, the solvent fumes discharged to the atmosphere pose an environmental hazard due to the interaction of solvents with the ozone layer. As such, alternative coating processes utilizing dry powders, high solids and waterborne solids have been developed to avoid the disadvantages associated with solvent based coatings.

In particular coating applications, such as a dry powder coating process, an electrostatic spray gun assembly having a positive polarity is utilized to apply dry powder solids to a product having a negative polarity. Due to the resultant mutual attraction of the positively charged coating particles and the negatively charged substrate, overspray is substantially reduced. After receiving the dry paint particles, the coated product is baked at a high temperature until the dry paint particles melt and flow about the product, thereby forming a continuous coating. Such systems require substantial investment for equipment and have limited use due in part to the required baking step. In many instances, it is often required to wash the product prior to powder coating. As a result, the wet product has to be dried prior to coating to minimize any surface interaction with the applied coating particulates. An extended period of time is often required to dry the product to provide a surface suitable for coating with a powder or paint. Among the products which can be powder coated, there are included metal, for example, steel, plastic, such as a thermoplastic, or thermoset, and wood.

High solids coating systems utilize a high viscosity paint emulsion having a high solids to solvent ratio. As a result, the paint emulsion is generally applied to a product with a high pressure spray nozzle which inherently produces a substantial amount of overspray. The coated product is subsequently cured in a separate drying area using a heat source such as an oven or heat lamps. As with the above-described powder coating systems, a high solids coating system requires a substantial investment for equipment and has limited use due to the required heating step.

In a waterborne solids wet system, the coating solids are suspended in a fluid having a relatively high water to solvent ratio. Although the equipment required for this type of coating system is generally less expensive and complex due to a lower curing temperature, the required drying times are generally much longer than with solvent or dry powder based coatings.

As stated, currently available collection systems are generally designed to discharge large quantities of air to the outside environment. Unfortunately, this results in higher energy costs since additional energy must be expended to recondition the indoor building air. In addition, the residual pollutants in the discharged air are closely regulated by local and federal agencies, oftentimes requiring the procurement of a plurality of costly permits and/or the payment of large fines. These energy and regulatory requirements oftentimes add considerable cost to the price of a finished product.

Over the last decade, the use of high solvent based coatings has drastically decreased due to the ever increasing number of regulatory restrictions on the emission levels of contaminated air into the environment. As such, the popularity of dry powder, high solids, waterborne and other alternative coatings has increased tremendously. Due to the high investment cost and limitations of the dry powder and high solids coatings, waterborne coatings stand out as the best alternative for economical use. As stated above, one of the major disadvantages of a waterborne coating system is the requisite longer drying cycle which results in substantially increased production costs.

As described above, various coating techniques are available for coating a wide variety of substrates in an economical and environmentally safe manner. As previously discussed, certain coating methods moreover, such as powder coating, require a clean dry substrate prior to the application of the powder coating composition. However, available methods for drying wet substrate after it has been washed to prepare it for powder or liquid coating often require times such as 2 hours.

It would be desirable therefor to provide improved procedures for effectively drying substrate such as metal, for example steel, plastic, or wood to facilitate the subsequent application and cure of protective materials, such as used in powder coating, or water based acrylates.

SUMMARY OF THE INVENTION

The present invention is based on the discovery that improved drying times for metal, plastic, or wood substrates which have been washed prior to being powder coated or painted, can be achieved by employing an automated air filtration and drying system as shown in copending application Ser. No. 08/783,070 filed Jan. 15, 1997 now U.S. Pat. No. 5,718,061. More specifically, the present invention incorporates an energy and environmental management system for controlling, monitoring and supervising the operation and performance of the air filtration and drying system, a capture apparatus for capturing and controlling airborne particulates, and a drying control module for rapidly drying wet substrate using a continuously filtered and dehumidified flow of recycled air. Advantageously, the automated air filtration and drying system of the present invention is adapted to drastically reduce the drying times currently experienced in production coating processes, and substantially reduce energy operating costs.

There is further provided by the present invention, a drying method for expeditiously effecting water removal from exposed wet surface of a metal, plastic or wood substrate, which drying method utilizes a drying system comprising a drying booth to receive wet substrate in a batchwise or continuous manner, and means for continuously generating and circulating within the drying booth, a dehumidified and filtered air stream having an RH value of at least about 9% at temperature up to about 105° F., which can be directed in a substantially parallel manner at a rate of at least 50ft per minute across wet substrate surface in the drying booth.

In a further aspect of the present invention, there is provided a method for coating a substrate in a stepwise manner, which comprises:

(1) washing the substrate;

(2) drying the substrate;

(3) applying a curable coating material selected from the group of powder and aqueous based paint to the substrate; and

(4) effecting the cure of the curable coating material applied to the substrate;

where drying the substrate in step (2) is achieved by utilizing a drying system comprising a drying booth to receive wet substrate in a batchwise or continuous manner, and means for continuously generating and circulating within the drying booth, a dehumidified and filtered air stream having an RH value of at least about 9% at temperature up to about 105° F., which can be directed in a substantially parallel manner at a rate of at least 50 ft per minute across wet substrate surface in the drying booth.

Preferably, metal substrate, dried in accordance with the practice of the invention, means metal substrate having a water vapor pressure in the range of about 0.15 to about 0.60 and preferably, 0.19 to about 0.50 (In. of Hg) as measured under ambient conditions in an atmosphere having an RH% of about 20 to about 50 and a temperature of about 60° F. to about 90° F. It has been found that dry metal substrate suitable for powder or liquid coating can be provided in about 2 to 10 minutes, in accordance with the practice of the present invention, utilizing the system of drying shown in copending application Ser. No. 08/783,070 filed Jan. 15, 1997.

As used hereinafter, the term metal, or metal substrate preferably includes steel in a variety of shapes and sizes, such as steel sheet, rod or a prefabricated structure. The term steel is more particularly defined in Grant and Hackh's Dictionary, fifth edition, {1987} McGraw-Hill Book Co. on page 553 which is incorporated herein by reference. The term plastic substrate includes thermoplastic polyetherimides and thermoset polyimides. Some of the plastic substrates which can be powder coated in accordance with the practice of the invention, are further shown in Grant and Hackh's Dictionary, fifth edition on page 455 and incorporated herein by reference. There are included among the powder coating materials which can be used to coat the aforementioned substrates dried in accordance with the practice of the present invention, powder coating compositions such as shown in U.S. Pat. No. 5,556,389 and patents cited therein which is incorporated herein by reference. Powder coating procedures which can be used are shown in the Encyclopedia of Polymer Science, Volume 3, pages 583-589, John Wiley and Sons (1985).

Among the water based paints which can be applied to various substrate as previously defined, there are preferably included, water based polymethacrylates, such as Lucite paint. However, water based compositions such as shown in U.S. Pat. Nos. 5,614,582; 5,141,983; and 4,692,483 also can be used.

The energy and environmental management system is an automated management and control system which is adapted to enhance the performance of the capture apparatus and the drying module while minimizing the energy consumption of the air filtration and drying system. In a typical application, the energy and environmental management system includes a host computer, a plurality of peripheral interface panels, a plurality of input/output interfaces and a number of sensors for monitoring and measuring a wide variety of conditions throughout the air filtration and drying system and associated spray booth. Examples of the aforesaid conditions are listed below:

a) Collection area face velocity.

b) First stage filtration static pressure.

c) Main filtration static pressure.

d) Ambient temperature.

e) Ambient humidity.

f) Induced humidity.

g) Elapsed real time.

h) Electrical service status (voltage, amperage, polarity).

I) Motor amperage draw.

j) Pre-filtration particulate count.

k) Post-filtration particulate count.

l) Pre-filtration gas phase.

m) Post-filtration gas phase.

n) Volatile organic compounds (presence, breakthrough).

The capture apparatus of the instant invention is adapted to effectively remove overspray contaminants from the air within a spray booth, thereby virtually eliminating the release of any deleterious contaminants into the atmosphere and surrounding work environment. Preferably, the capture apparatus is designed to provide a minimum airflow of 100 feet per minute across the cross-sectional area of the spray booth collection area and a capture wall capacity of 10,000 to 100,000 CFM at 1.5 to 3.0″ W.G.

The capture apparatus is equipped with a blower, such as a backward inclined curved vane rotary blower impeller or the like, for drawing contaminated air from the collection area of the spray booth into a dry type multi-stage filtration system, wherein the filtered air is either expelled into adjacent work areas during a painting or regeneration cycle or returned into the collection area during a drying cycle, under control of a computer controlled damper system.

The energy and environmental management system includes a process control system for enhancing the performance of the capture apparatus by monitoring and controlling the operation of the blower motor. More specifically, the process control system incorporates a motor amperage feedback loop and variable frequency drive system, such as the ACS 500 drive system manufactured by ABB Industrial Systems, Inc., for regulating the speed (rpm) of the blower motor to compensate for increased static pressure due to filtration loading. As a result, the present invention automatically provides constant regulation of airflow volume and face velocity regardless of filter loading, thereby reducing required drying times. Any amperage increases of 5% or more above preset amperage conditions (application specific) are detected by the process control system and result in the initiation of a self-diagnostic subroutine, the production of a record data log entry for future analysis and the generation of a preprogrammed service request.

The dry type multi-stage filtration system incorporates a highly efficient serial arrangement of filtering components including arrestor pads, secondary and primary prefilters, a main high efficiency filter and an odor absorbing gas phase filter. Detailed descriptions of the filtering components utilized in the preferred embodiment of the present invention are set forth in the following paragraph.

The arrestor pads are formed of a synthetic poly fiber material or have a multi-layered construction, and are composed of slit and expanded heavy water resistant kraft with multistage designed baffle openings and duo-density singed synthetic backing. The secondary prefilters are constructed of a pleated media enclosed in a water resistant cardboard frame and has a 25 to 60% nominal efficiency (arrestance) on ASHRAE TEST 52-76 Dust Spot, which, as established by the American Society for Heating, Refrigeration and Air Conditioning Engineers, is a measure of the ability of a filter to reduce soiling of both fabrics and building interior surfaces. Similarly, the primary prefilter is formed of a 35 to 75% minimum ASHRAE pleated media enclosed in a water resistant cardboard frame. The main filter includes a high efficiency pleated media or High Efficiency Particulate Air Filter (hereinafter referred to as H.E.P.A.) having a 90 to 99% efficiency on 0.3 micron particulate and a penetration efficiency of no more than 10% on 0.3 micron particulate in accordance with ASHRAE sodium flame method test B53928/M7605. Finally, the odor absorbing gas phase filter, which provides gas control to 0.00003 microns in size, employs coarse fiber substrates with an 80% retention porous structure in reticulated carbon media, wherein one cubic foot of substrate provides approximately 2 million square feet of surface area for adsorption. As should be readily apparent to one of ordinary skill in the art, many other filtering components or combinations thereof may be utilized in lieu of those described above without departing from the scope of the present invention.

Various types of dehumidifying/drying control modules may be incorporated into the present invention depending upon specific application requirements and conditions. A first type may incorporate a regenerative twin tower dryer, a rotary continuous air dryer, a rotary refrigerant continuous air dryer or a desiccant/deliquescent multiplex unit. This type of drying module is adapted to direct a continuously recycled, heated and dehumidified flow of air over a coated product to absorb and eliminate moisture. A second type may incorporate a refrigeration based dehumidification drying system. This type of system recirculates air that is chilled below its dew point temperature to give up moisture in the form of condensation on a nearby surface.

Advantageously, in either type of system, the contaminant concentration and humidity of the recycled air is continuously lowered as it cycles over the coated product, through the capture apparatus and through the drying module. In applications requiring continuous operation and desiccant media, regeneration of the media occurs during system down or lag times. Contrastingly, refrigerant dryers are adapted to be operated continuously and thereby require no regenerative stage.

In a first embodiment of the present invention, a regenerative twin tower dryer is utilized to heat and dehumidify the spray booth air during the drying process. As known in the art, a regenerative twin tower dryer utilizes a pair of adsorption columns in an alternating manner, thereby allowing one column to be in use while the second is regenerating. The geometry, size and desiccant bed configuration of the regenerative twin tower dryer system is carefully tailored in accordance with application specific criteria such as adsorption capacity, humid air velocity, retention time, operating cycle, drying efficiency, energy consumption, cure rate and the like. Further, minimum and maximum performance parameters are specifically assigned to accommodate specific operating variables such as media generation rate, meteorological conditions and spray equipment performance.

In a second embodiment of the present invention, a cooling or refrigeration based dehumidification unit is utilized to cool and dehumidify the spray booth air during the drying process. As mentioned, recirculated air that is chilled below its dew point temperature gives up moisture in the form of condensation on the nearest surface it encounters. Thus, the air in the system is dehumidified during the cooling and condensing cycle. The cooling and refrigeration unit is comprised of: 1) an evaporator or cooling coil; 2) a compressor; 3) a condenser or reheat coil; 4) a liquid refrigerant or receiver tank; and 5) an expansion tank. This embodiment may be used to pretreat the product surface (i.e. remove moisture prior to the application of a waterborne coating) and/or post-treat the product surface (i.e. remove the application after the application of the waterborne coating).

In providing a drying module that does not incorporate a heating system, this particular embodiment has the further advantage of more easily meeting existing fire safety standards. For example, both NFPA and OSHA provide various regulations regarding the use of heat or hot surfaces in or near a spray both. (See e.g., OSHA §1910.107 and NFPA 33). Thus, this embodiment provides an effective means of drying while providing a safe environment.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will become readily apparent upon reading the following detailed description and upon reference to the drawings in which:

FIG. 1 illustrates the painting cycle airflow path through an automated air filtration and drying system in accordance with a second embodiment of the present invention;

FIG. 2 illustrates an automated air filtration and drying system for a spray booth in accordance with a first embodiment of the present invention;

FIG. 3 illustrates the painting cycle airflow path through the automated air filtration and drying system of FIG. 2;

FIG. 4 illustrates the drying cycle airflow path through the automated air filtration and drying system of FIG. 2;

FIG. 5 illustrates the formation of an overspray impact pattern on the collection face of a prior art overspray filtration system;

FIG. 6 is a top view of a quadrant diffusion system in accordance with the present invention;

FIG. 7 is a front elevational view of the quadrant diffusion system of FIG. 6;

FIG. 8 is a front view of the quadrant diffusion system with the front and rear panels mutually centered;

FIG. 9 is a front view of quadrant diffusion system with the rear panel shifted in a negative direction along the x and y-axes;

FIG. 10 illustrates a specific application of the quadrant diffusion system in the automated air filtration and drying system of FIGS. 1 and 2;

FIG. 11 is a block diagram of the energy and environmental management system;

FIG. 12 is a bar graph comparing drying times for a product in and out of a booth built in accordance with this invention;

FIG. 13 is a bar graph comparing drying times for a product in and out of a booth built in accordance with this invention;

FIG. 14 is a bar graph comparing drying times for a product in and out of a booth built in accordance with this invention;

FIG. 15 is a bar graph comparing drying times for a product in and out of a booth built in accordance with this invention;

FIG. 16 illustrates an automated air filtration and drying system for a spray booth incorporating a horizontally mounted impeller fan device in accordance with this invention;

FIG. 17 illustrates an automated air filtration and drying system that incorporate a remote condenser and drying booth with an open wall in accordance with this invention;

FIG. 18 illustrates the temperature and humidity control components in accordance with this invention;

FIG. 19 illustrates the powder coating of a substrate, such as steel in accordance with the practice of the invention; and

FIG. 20 illustrates the coating of a substrate in accordance with the practice of the invention with a water based paint.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now specifically to the drawings, in accordance with the present invention, there is illustrated a first (FIGS. 2-4) and second (FIG. 1) embodiment of an automated filtration and drying system, generally designated as 10, wherein like reference numbers refer to like parts throughout the drawings.

As illustrated in FIG. 2, the automated filtration and drying system 10 is adapted to be utilized in conjunction with a spray booth 12 to remove any overspray produced while coating a product 14 with a spray gun 16 or other suitable applicator.

Referring to FIGS. 1-4, contaminated air is drawn into a capture apparatus 19 within the automated filtration and drying system 10, as indicated by the directional arrows 18, by a backward inclined curved vane blower impeller 20 and associated blower motor 22. A computer regulated motor amperage feedback loop, including a pair of first stage static pressure sensors 24, 26, a pair of main filter static pressure sensors 28, 30, a motor amperage draw/rpm sensor 32 and a computer controlled variable frequency drive system 34, is provided to regulate the speed of the blower motor 22 to compensate for increased static pressure due to filtration loading, and variations in supply voltage. As indicated in FIG. 3, the outputs of the static pressure sensors 24, 26, 28, 30 and the output of the motor amperage draw/rpm sensor 32 are provided to a system host computer 36 through a peripheral interface panel assembly 38. In response thereto, the host computer 36 provides the appropriate speed compensation signal to the variable frequency drive system 34, again through the peripheral interface panel assembly 38. More specifically, as the total differential static pressure between the pair of first stage static pressure sensors 24, 26 and the pair of main filter static pressure sensors 28, 30 increases due to filtration loading, as determined by the host computer 36, the speed of the blower motor 22 is increased accordingly via the variable frequency drive system 24, thereby providing a predetermined (application specific) constant airflow volume and airflow velocity through the capture apparatus 19. Analogously, the speed of the blower motor 22 is modified in accordance with variations in the supply voltage to again provide the requisite constant airflow volume and velocity. The motor speed may be adjusted in a continuous manner or in response to predetermined variations in static pressure levels.

Static pressure sensors 24, 26, 28, 30 preferably comprise a Pitot tube having a closed end and a plurality of radial holes disposed proximate a static pressure tip, wherein the holes are presented to the airflow stream at 90 degrees, thereby providing an accurate static pressure reading. The static pressure tip is connected through flexible tubing to a pressure transducer or other suitable pressure indicating unit which is adapted to supply a 4-20 mA signal to host computer 36 through peripheral interface panel assembly 38.

Again, referring to FIGS. 1-4, the overspray contaminants are captured and removed from the incoming stream of contaminated air 18 as it passes into and through the capture apparatus 19. More specifically, as indicated by the flow of directional arrows, the blower impeller 20 is utilized to draw contaminated spray booth air through a dry type multi-stage filtration system comprising an arrestor pad arrangement 40, a secondary prefilter arrangement 42, a primary prefilter 44, a main H.E.P.A. filter 46 and a gas separation filter 48.

After passing through the multi-stage filtration system, the filtered air is either expelled into the work environment through a painting cycle discharge port 50, or passed through a drying module, generally designated as 52, and returned to the spray booth 12 through a drying cycle air outlet 54. As illustrated in FIGS. 1-4, a damper actuator 56, preferably including an electric motor drive and associated linkage, is utilized to regulate the position of a damper door 58 under control of host computer 36, thereby selectively directing the filtered air through the painting cycle discharge port 50 or into the drying module 52. As stated above, the drying module 52 may comprise either a heat based system (FIGS. 2-4) or a refrigeration based system (FIG. 1).

The invention, as shown in FIGS. 1-4 and 16, also has the additional distinct advantage of providing an automated filtration and drying system 10 that is easily mounted, or coupled, to a drying booth 12. These embodiments only require a single interface wall unit between the drying booth 12 and the filtration and drying system 10. Thus the design, manufacture and usability of the drying booth is greatly enhanced. Moreover, the interface wall need only provide an opening for removing air 18 and returning air 54. The interface wall unit may be comprised of filtering devices 40, 42 and 64 and a return duct 54. Therefore, unlike other systems, these embodiments do not require underground or roof mounted equipment.

Referring now to FIGS. 2-4, the first embodiment (which incorporates a heat based system) is illustrated. This system preferably utilizes a regenerative twin tower dryer including hydro-absorber banks 60, regenerator assembly 62 and a computer controlled heating element 63 which may be separate from or integral with regenerator assembly 62.

The painting cycle airflow path through the present invention is illustrated in FIG. 3. As indicated by directional arrows 18, air, which has been contaminated by overspray, is drawn into the automated air filtration and drying system 10 by the blower impeller 20 and subsequently passes through the arrestor pad arrangement 40, the secondary prefilter arrangement 42 and a quadrant diffusion system 64. After advancing past a sensor array area 66, the partially filtered air passes through the primary prefilter 44, the main high efficiency particulate air filter (H.E.P.A.) 46, the gas separation filter 48 and the blower impeller 20. During the painting cycle, the damper door 58 is secured over the intake 68 of the drying module 52, and the filtered air is directed into the work environment through the painting cycle discharge port 50.

Referring to FIG. 16, an additional embodiment is shown. This embodiment is essentially the same as those shown in FIGS. 1-4, except that the blower impeller 200 (20 of FIGS. 1-4) is horizontally mounted on the rear wall rather than vertically mounted on the ceiling. It is envisioned that either a heat based or refrigeration based drying system could be utilized therein.

As evidenced by a comparison of FIGS. 3 and 4, the initial portions of the drying cycle and painting cycle airflow paths are identical. Namely, referring now specifically to FIG. 4, air from the spray booth is drawn by the blower impeller 20 through the arrestor pad arrangement 40, the secondary prefilter arrangement 42, the quadrant diffusion system 64, the sensor array area 66, the primary prefilter 44, the main H.E.P.A. filter 46 and the gas separation filter 48. Unlike the painting cycle airflow path, however, the filtered air is directed into the drying module 52 during the drying cycle after passing through the blower impeller 20. More specifically, during the drying cycle, the damper door 58 is secured over the painting cycle discharge port 50, and the filtered air is conducted into the drying module 52 through the intake 68 thereof. After flowing through the hydro-absorber banks 60, the regenerator assembly 62 and the computer controlled heating element 63 of the drying module, the filtered, heated and dehumidified air exits the drying module through the drying cycle air outlet 54 and passes into the spray booth. The filtered, heated and dehumidified air is subsequently passed over a coated product which is drying within the spray booth to further absorb and eliminate moisture therefrom, before again being drawn into the air filtration and drying system 10 by the blower impeller 20. Advantageously, the spray booth air is continuously filtered, dehumidified and heated as it is recycled through the multi-stage filtration system and the drying module 52, thereby drastically reducing the drying times required for waterborne based coatings.

Referring now to FIG. 1, a second embodiment (which incorporates a refrigeration based system) is illustrated. This system is functionally equivalent to the first embodiment with the exception of the components located within the drying module 52. The air filtering mechanisms are equivalent in both embodiments. Thus, the two embodiments will only function differently when damper door 58 is closed and the air flow is forced into the drying module 52 (see FIGS. 1 and 4). Under this second embodiment, the hydro-absorber bank 60, the regenerator assembly, and the computer controlled heating element 63 of the first embodiment (FIGS. 2-4) are removed. Instead, the present system will typically utilize components that may include a compressor 71, a liquid refrigerant or receiver tank 73, an expansion valve 75, a condenser or reheat coil 77, an evaporator or cooling coil 79 and a drain 81.

As noted, when the damper door 58 is closed the air is forced into the drying module 52. The air, which is therein subjected to a refrigeration system, is chilled below its dew point temperature to then give up moisture in the form of condensation on the nearest surface it encounters. The dryer air is then passed back into the spray booth via outlet 54 where it acts as a sponge absorbing the product moisture. The components that make up the refrigeration system are typical of the present art.

Referring now to FIG. 17, a drying/filtration system is depicted that further includes a remote condenser unit 83 and a humidifier 91. The remote condenser unit 83 includes a condenser coil 87 and a cooling fan 85. The operation of the remote condenser unit 83 and the humidifier is further detailed in FIG. 18. FIG. 18 depicts a dehumidification system 52 for maintaining a predetermined temperature and humidity that may be located within the drying/filtration module. Moist air 212 first enters into the enclosed passageway 220 and is cooled by evaporator 79. In addition to cooling, evaporator 79 removes the moisture from the air to create a cool dry air 214. The moisture from the evaporator 79 is thereafter drained away (not shown). After the air is cooled, it passes through a reheat coil 77, which creates a warm dry air 216. Warm dry air 216 can then be passed back into the drying booth to collect moisture from a wet coated surface. Compressor 271 drives the system by pumping a refrigerant fluid 210 into the evaporator 79. Because this process warms up the refrigerant fluid, the reheat coil 77 can be used to reheat the cold air to a suitable temperature. However, if the refrigerant gets too hot, a solenoid valve 222 or the like can be used to redirect the refrigerant to a remote condenser 87, which is used to cool the refrigerant. The remote condenser 87 is located exterior to the drying/filtration system such that any unwanted heat can be removed from the system and exhausted into the work environment. A fan 85 may be used to further enhance the cooling effect of the remote condenser 87. Air temperature may therefore be regulated by a thermostat, PLC, or similar device (not shown). Based on a preset temperature, the solenoid 222 will decide whether or not to sent refrigerant to the reheat coil 77 or the remote condenser 87.

As air being continuously circulated throughout the system, the humidity is continuously dropping. A humidifier 91 may be used to introduce humidity back into the system as needed to control the level of humidity in the system. Any known humidity detection system may be used in conjunction with the humidifier to allow a user to preset the humidity level. Thus, these components allow the user to control the drying environment by preselecting the exact temperature and humidity. Because different types of paint require different drying conditions, such control in critical in obtaining across-the-board drying efficiency. With the disclosed components, this system can readily provide a temperature anywhere in the range of 45 to 125 degrees Fahrenheit and a relative humidity (RH) anywhere in the range of 25 to 95 percent. Choosing a particular system setting (e.g., 50° F., 45% RH) will depend on various factors including paint thickness and paint type. While it is envisioned that this system will accelerate drying for almost any water-based paint with a coating thickness of from 0.1 to 15 MILS, it is not necessarily limited to such applications. It is also envisioned that performance outside of the above stated ranges could be reached by making relatively simple modifications to the drying/filtration system.

Referring now to FIGS. 1-4 and 11, a volatile organic compound (VOC) breakthrough sensor 70 is utilized to detect the presence of organic solvent vapors and other volatile or hazardous vapors. The VOC breakthrough sensor 70 includes a sensing element, preferably having a vapor sensitive conductivity or the like, which is adapted to transmit a 420 mA signal to the host computer 36 through the peripheral interface panel assembly 38. If the host computer 36 determines that dangerous vapors are present in the system during the painting or drying cycles, in response to the output of the VOC breakthrough sensor 70, it will actuate the appropriate visual and/or audio alarms to advise personnel that a hazardous compound is present in the system and that immediate maintenance, perhaps due to a malfunctioning or improperly installed gas separation filter 48, is required.

The output of the VOC breakthrough sensor 70 is further utilized to control the operation of the damper actuator 56 and the drying module 52, and the associated position of the damper door 58. More specifically, in response to a positive reading from the VOC breakthrough sensor 70 (VOC present), the host computer 36 sends a drying cycle disable signal through the peripheral interface panel assembly 38 to a dry system interlock 72, comprising an electromechanical relay or the like, resulting in the shut down of the drying module 52 and the securement of the damper door 58 over the intake 68 of the drying module 52 via damper actuator 56. Analogously, when a VOC is not detected, the VOC breakthrough sensor 70 outputs a negative reading to the dry system interlock 72, thereby enabling the damper door 58 and allowing the initiation or continuation of a drying cycle. Advantageously, the operational longevity of the desiccant within the hydro-absorber banks 60 (FIGS. 2-4) is greatly increased by preventing VOC contaminated air from entering the drying module 52.

An outlet humidity sensor 74 and ambient humidity sensor 76 are utilized to monitor and control the operation of the drying module 52. The outlet humidity and ambient humidity sensors 74, 76 preferably include a humidity sensitive element, having a humidity responsive AC resistance, and a thermistor which is adapted to compensate for the temperature dependency of the humidity sensitive element. Each humidity sensor provides a 4-20 mA signal which is fed to the host computer 36 through the peripheral interface panel assembly 38.

During the drying cycle, the outputs of the outlet and ambient humidity sensors 74, 76 provide the host computer 36 with data corresponding to the humidity of the air that is flowing out of the drying module 52 and into the capture apparatus 19, respectively. When the humidity level measured by one or both of the humidity sensors falls below a predetermined humidity limit, indicating that a coated product within the spray booth 12 (FIG. 2) has dried/cured to a sufficient degree, the drying cycle is disabled via the dry system interlock 72, and the damper door 58 is subsequently secured over the intake 68 of the drying module 52. Correspondingly, the drying cycle is enabled while the measured humidity level remains above the predetermined humidity limit during the drying cycle. In a similar manner, if the humidity level fails to reach the drying cycle humidity limit after a predetermined amount of time has elapsed, indicating possible system malfunction, the drying cycle is disabled.

The present invention incorporates outlet and ambient temperature sensors 78, 80, to provide the host computer 36 with outlet and ambient airflow temperature measurements, respectively. Preferably, each temperature sensor includes a thermistor and related circuitry to supply a 4-20 mA signal to the host computer 36 through the peripheral interface panel assembly 38. If the outlet and/or ambient temperature measurements deviate sufficiently from a predetermined, application specific, optimum drying temperature during the drying cycle, the host computer 36 transmits the necessary temperature adjustment signal to a temperature controller 82 which subsequently provides the appropriate temperature adjustment signal to the computer controlled heating element 63 (FIGS. 2-4) or the refrigeration system (FIG. 1) located within the drying module 52.

Sensor area 66 further includes an airflow sensor 84, for measuring input airflow in cubic feet per minute (CFM), and an air velocity sensor 86 for measuring input air velocity in feet per minute (FPM), wherein the sensor outputs are supplied to host computer 36 through peripheral interface panel assembly 38. Preferably, the airflow sensor 84 and air velocity sensor 86 include an auto sensor tube assembly similar in construction to the above-described static pressure sensors 24, 26, 28, and 30, although any appropriate sensor technology may be utilized. The data obtained by sensors 84 and 86 is primarily utilized for system monitoring purposes. However, since airflow and air velocity are directly related to the degree of filtration loading, the outputs of sensors 84, 86 may be utilized by the host computer 36 in lieu of or in conjunction with the outputs of the static pressure sensors 24, 26, 28, 30, to thereby control the speed of the blower motor 22 via the variable frequency drive system 24.

Particulate sensors 88, 90, of the type known in the art, are utilized to provide the host computer 36 with measurements of the upstream (unfiltered) and downstream (filtered) particulate concentrations, respectively. If the particulate concentrations deviate from expected values, or if decontamination efficiency of the capture apparatus 19 falls below a predetermined minimum level, the host computer 36 is adapted to output the necessary status information to a system operator.

Referring to FIG. 11 (and 2), there is illustrated, in partial block form, the energy and environmental management system according to the present invention. As stated above, the energy and environmental management system includes a host computer 36 for monitoring and controlling the operation of the automated air filtration and drying system 10. A peripheral interface panel assembly 38 is utilized to direct the system information received from the plethora of sensors disposed within the spray booth 12, the capture apparatus 19 and the drying module 52 into the host computer 36 and to output any requisite control information to the appropriate computer actuated/controlled system components.

A display 92 is utilized to provide an operator with a visual indication of some or all of the sensor readings received by the host computer 36, thereby allowing the operator to monitor the operational status of the automated air filtration and drying system of the present invention. Preferably, a datalog of the received sensor readings is stored for future analysis in a data storage system 93 such as a hard disk drive or the like.

The energy and environmental management system includes an operator control panel 94 for controlling the basic operation of the air filtration and drying system, wherein the blower motor 22 and system controls are activated or deactivated by the manually actuated run and stop buttons 96 and 98, respectively, and the drying cycle is activated or deactivated by the manually actuated dry and paint buttons 100 and 102, respectively. The operator control panel 94 further includes a plurality of highly visible, multicolored status lights 104 which are adapted to quickly provide a system operator with system status information corresponding to static pressure, blower motor rpm, airflow, air velocity, outlet temperature, ambient temperature, outlet humidity, ambient humidity, VOC presence, particulate concentration and the like. Preferably, a green status light is utilized to indicate normal system operation within preset ranges, a yellow status light is utilized to indicate that the system is nearing diagnostic or maintenance stages and a red (flashing) status light is utilized to indicate system malfunction, system shutdown or the necessity of immediate system maintenance/repair. A keyboard 106 is provided on the operator control panel 94 for data analysis, record keeping and operational or application specific program updates/modifications, such as outlet temperature and humidity requirements, blower motor speeds and the like.

Referring now to FIG. 5, the airflow across the collection face 108 of currently available overspray filtration systems oftentimes produces an unbalanced overspray impact pattern 110 on the collection face 108 as the overspray is drawn into the filtration system after passing around a product 112 being coated. As the underlying portion of the collection face 108 begins to clog, thereby preventing air from being drawn therethrough, the periphery of the overspray impact pattern 110 migrates outward as indicated by directional arrows 114.

To prevent the formation of such an unbalanced overspray impact pattern, the present invention provides a novel quadrant diffusion system 64 for producing a balanced flow of air across the collection face of the automated air filtration and drying system 10. As previously described with respect to FIGS. 1 and 3-4, the quadrant diffusion system 64 is preferably disposed behind the arrestor pad arrangement 40 and secondary prefilter arrangement 42.

As illustrated in FIGS. 6-10, the quadrant diffusion system 64 includes at least one pair of overlapping, parallel panels 116, 118, each including a patterned series of apertures therethrough, wherein the pattern of apertures in each panel offers a minimal restriction to airflow. Although the front panel 116 and the rear panel 118 include the same number of apertures, the apertures on the rear panel incorporate a slightly larger center to center pattern. As such, the nominal flow center of air through the panels 116, 118 may be altered by moving the panels 116, 118 slightly off center from one another as illustrated in FIG. 7. Preferably, the front panel 116 remains stationary and the rear panel 118 is shifted as necessary along the x and y-axes to provide the required flow center of air. For example, as shown in FIG. 8, the nominal flow center of air occurs at aperture 120 when the panels 116, 118 are mutually centered. If the rear panel 118 is shifted in a negative direction along the x and y-axes, as depicted in FIG. 9, the nominal flow center of air is shifted toward the upper right region of the panel arrangement. As should be readily apparent, the nominal flow center through the parallel panels may be shifted as necessary in accordance to application specific requirements by altering the relative orientation of the front and rear panels 116, 118.

An application of the quadrant diffusion system 64, incorporating nine pairs of overlapping, parallel panels to balance the flow over the collection face (arrestor pad arrangement 40) of the air filtration and drying system 10, is illustrated in FIG. 10. More specifically, nine pairs of parallel panels 116, 118, are arranged in a three-by-three matrix behind the arrestor pad arrangement 40 and secondary prefilter arrangement 42, with the nominal flow center of air through each pair of panels 116, 118 adjusted to provide the airflow pattern indicated by directional arrows 124. Advantageously, the resultant overspray impact pattern produced while coating product 14 is distributed substantially equally over the entire collection face area of the arrestor pad arrangement 40, due to the balanced airflow provided by the quadrant diffusion system 64.

Referring now to FIGS. 12-15, several bar graphs are shown comparing drying times of a product in and out of a booth built in accordance with this invention. In each of the graphs represented in these figures, the clear bars represent drying time wherein the booth is utilized and the cross-hatched bars represent drying times wherein the booth is not utilized.

FIG. 12, which depicts the drying time of a round casting at a wetness of 4-5 MILS, shows that it only took 12.5 minutes for a casting to completely dry when placed in the booth as opposed to 69 minutes when not placed in the booth.

FIG. 13, which depicts the drying time of a round casting at 4-6 MILS with a fan blowing on the casting, shows that it only took 11.5 minutes for a casting to completely dry when placed in the booth as opposed to 69 minutes when not placed in the booth.

FIG. 14, which depicts the drying time for an assembled pump (2800 lbs.) at 6-8 MILS, shows that it only took 42.5 minutes for the pump to completely dry when placed in the booth as opposed to 123 minutes when not placed in the booth.

FIG. 15, which depicts the drying time for an assembled pump (2800 lbs.) at 3.5-5 MILS, shows that it only took 16.5 minutes for the pump to completely dry in the booth as opposed to 90 minutes when not placed in the booth.

FIGS. 19 and 20 show total capture systems of coating various substrates with powder or water based paint. There are shown substrate introduction into a washing stage which can include an optional preclean, a chemical wash, a rinse with potable city or deionized water, additional rinses with deionized water and virgin deionized water, and an air blow off. The wet substrate is then introduced into the drying stage where it experiences a rapid dry in accordance with the practice of the invention followed by a maintain dry stage. The application stage involves either the powder coating of the dry substrate, as shown in FIG. 19, or the liquid application as shown in FIG. 20. Curing of the applied coating is effected by an oven cure as shown in FIG. 19 or a paint dry as shown in FIG. 20. The coated substrate which can be metal, such as steel, plastic or wood can be prepared for storage or shipment.

As a result of the above described improvements in the temperature and humidity control system using a separate condenser and humidifier component, means are provided for achieving more control over proper drying by being able to preset the required RH and temperature. These RH and temperature control features have been found to be particularly important when affecting the drying of substrates which have been washed prior to being powder coated or painted, where such substrates, such as metal, plastic or wood, can have a wide range of thicknesses and drying characteristics.

While the following example illustrates the effectiveness of the practice of the method of the present invention to dry previously washed steel substrate prior to being powder coated a substantially similar drying procedure can be used to paint the substrate:

A strip of wet steel sheet having a surface area of about 10 Sq. Ft is thoroughly washed and rinsed in distilled water. The wet steel having an initial surface water vapor pressure of about 1.67 (In.Hg) is introduced into booth 12 shown in FIG. 2. The wet steel strip is positioned to allow full exposure of its surface to a filtered air stream in a substantially parallel manner within the booth. The filtered air steam has a surface velocity of at least 50 feet per minute, and an RH value of about 25% at 81° F. The air stream impinges on the wet steel surface in a substantially parallel manner for a period of about 10 minutes. There is obtained, a steel sheet having an average water vapor pressure of about 0.30 (In.Hg) under ambient conditions within the booth. The dried steel substrate is electrostaticly treated with charged powder comprising a thermosetting resinous composition which is subsequently cured by a standard procedure, such as shown by J. M. Lucas in U.S. Pat. No. 5,567,468. There is obtained steel substrate uniformly coated with cured resin.

While the above example is directed to the drying of a particular substrate, such as steel, it should be understood that the present invention also can be used to dry the surfaces of plastic and wood which can thereafter be powder coated, or painted. However, those skilled in the art would also recognize that in particular situations, RH values can vary depending upon the particular location and time a measurement is made. For example, the temperature at which the condenser is run, or whether the RH is based on the moisture level of the air stream evolving directly from the dryer system at 10 and return at 54 shown in FIG. 1, or whether the RH is measured within the booth which can have a totally different value based on the initial wetness and volume of moisture removed while the air stream impinges the substrate while it is drying within the booth.

The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of this invention as defined by the accompanying claims. 

What is claimed is:
 1. A method for effecting water removal from an exposed wet surface of a substrate selected from the group consisting of metal, plastic, and wood, the method comprising the steps of: washing the substrate; placing the substrate in a drying booth in a batchwise or continuous manner; drying the substrate by continuously generating and circulating within the drying booth, a dehumidified and filtered air stream, wherein the air stream is directed in a substantially parallel manner at a rate of at least 50 ft per minute across the substrate surface in the drying booth and has an RH value of at least about 9% at a temperature up to 105° F.; and providing at least one humidity sensing device within the drying booth to monitor an RH value of the air stream and disable the circulation of the air stream within the drying booth when the RH value of the air stream reaches a predetermined value.
 2. The method in accordance with claim 1, where water is removed from an exposed wet surface of steel.
 3. The method in accordance with claim 1, further comprising electrostatically coating dry steel substrate with charged powder which is thereafter cured.
 4. The method in accordance with claim 1, further comprising painting dry steel substrate with an aqueous based air curable paint after the drying step.
 5. The method in accordance with claim 1, wherein the substrate is a dry thermoset plastic.
 6. The method in accordance with claim 5, wherein the dry thermoset plastic substrate is a polyimide.
 7. The method in accordance with claim 1, further comprising coating the substrate with a curable material selected from the group consisting of a heat curable powder coating composition and an air curable aqueous based paint after the drying step.
 8. A method for removing moisture from an exposed wet surface of a substrate, the method comprising the following steps: wetting the substrate; placing the substrate in a drying booth in a batchwise or continuous manner; drying the substrate by continuously generating and circulating within the drying booth, a dehumidified and filtered air stream having a temperature up to about 105° F.; selecting and maintaining an RH value of the air stream of at least about 9% using a device within the drying booth; diverting the circulation of the air stream from the drying booth when the RH value of the air stream reaches a predetermined value; and coating the substrate approximately less than ten minutes after the drying step.
 9. The method in accordance with claim 8, wherein the coating step comprises the step of coating dry steel substrate with charged powder.
 10. The method in accordance with claim 8, wherein the coating step comprises the step of painting dry steel substrate with an aqueous based air curable paint.
 11. The method in accordance with claim 8, wherein the substrate is a dry thermoset plastic.
 12. The method in accordance with claim 11, wherein the dry thermoset plastic substrate is a polyimide.
 13. The method in accordance with claim 8, wherein the coating step comprises the step of coating the substrate with a curable material selected from the group consisting of a heat curable powder coating composition and an air curable aqueous based paint. 